Plasma chambers are used for a variety of processes, e.g., cleaning a wafer, depositing materials on a wafer, etc. Plasma is used to perform the processes. For example, a radio frequency (RF) generator generates an RF signal to transfer to a plasma chamber to generate plasma within the plasma chamber. The RF generator may be a 2 megahertz (MHz) RF generator, a 27 MHz RF generator, or a 60 MHz RF generator.
Another one of the processes includes etching a wafer. However, when a wafer is etched in a plasma chamber, rate of etching the wafer varies over time within the plasma chamber. For example, there is an 0.85% etch rate change when the 27 MHz RF generator is used to supply RF power to a plasma chamber to etch a wafer. As another example, there is a 1.08% etch rate change when the 60 MHz RF generator is used to supply RF power to a plasma chamber to etch a wafer.
Moreover, when a wafer is etched in multiple plasma chambers, different etch rates may be applied on the wafer. For example, there may be a 3.3% variability in etch rate chamber-to-chamber when the 27 MHz RF generator is used to supply RF power to a plasma chamber to etch a wafer. As another example, there may be a 4.8% variability in an etch rate chamber-to-chamber when the 60 MHz RF generator is used to supply RF power to a plasma chamber to etch a wafer.
It is in this context that embodiments described in the present disclosure arise.